פירוש על עבודה זרה 66:11

White and black glazed vessels do not absorb the taste of the wine, but the green one’s might, so they are prohibited. And cracks will let the taste go into the vessel, so they are prohibited.

This whole section is an extended difficulty on Meremar, a late Babylonian sage. Meremar allowed all glazed vessels that had been used with non-Jewish wine. He seemed to think that such vessels do not absorb. But when it came to vessels that had been used with hametz before Pesah, he ruled much more strictly, prohibiting all of them. He saw that they “sweat,” meaning they emit liquid when heated, and therefore he assumed that they also absorb. And once an earthenware vessel has absorbed taste, there is no way to “kasher” it.